Vowel recognition is determined by two acoustic energy bands we call 1st and 2nd formants (i.e. F1 and F2). We can identify three other formants that cluster to form what we refer to as the Singer’s Formant. The subject of this particular post is the 2nd Formant or F2 for short.
The following vowel formant chart below gives the center values for the formants of the most common vowels.
A slight alteration of these values, +/- 20 Hz will not change the vowel drastically in terms of recognition. However such a modification may help tune the vowel more precisely to the relevant harmonics of the sung pitch (which are fixed, i.e. unalterable). As pitch rises or falls, it becomes easier to tune one formant more easily than the other. Sometimes fundamental frequency will rise above F1 and so, F1 can no longer coincide with any of the harmonics of the sung pitch. In such a case, F2 becomes the more viable formant. Such is the case in the female middle voice and in the traditional male upper voice (counter-tenors voices behave similarly to female voices). It is no coincidence that the female middle voice and the male upper voice are the most challenging areas for the average singer.
The primary reason is the following: singers, like everyone else feel a strong attachment to their speaking voices, which is F1 dominant for both males and females. F2 resonance simply feels foreign relative to the speaking voice.
When the F2 area is reached, singers are aware that something must be altered in order for the voice to feel coordinated. There are fundamentally four choices in descending order of efficiency:
1) *Covered tone: Maintain balanced phonation (i.e. excellent closure/weight balance) and slightly modify the vowel to encourage F2. This is the best choice. But the new resonance will feel a little strange at first, as if the singer were abandoning natural speech. In fact, the singer would be abandoning the acoustic pattern of daily speech. However, if the modification is done well (particularly if phonation balance is maintained), the singer does not feel a great difference from F1 dominance to F2 dominance.
*The term covered is deceptive. It is more appropriate to the area of C#4 to E4 and C5 to E5 in male and female voices respectively. The rounding of the lips that define the term, covered, lowers both formants, a strategy that works in the lower passaggio. This is not efficient in that the desired effect at the higher points of the acoustic passaggi, around F4 and F5, is to lower one formant and raise the other. In such a situation, I recommend a smiled schwa as in the inhale before a sneeze.
2) Open tone: Maintain balanced phonation and modify the vowel considerably to follow F1 (maintaining the speaking voice). This may sound slightly awkward because the vowel modification might sound too extreme. This is however not altogether bad. In this particular case, to maintain F1 dominance beyond the F1 threshold has the bad result of causing the larynx to raise, robbing the singer of natural warmth. The resulting sound will be at best, one-sided (chiaro without enough scuro), and at the extreme, shrill! Still, the resonance adjustment would be viable and would give presence to the voice.
3) Spread tone: Losing the phonation balance because the resonance adjustment causes the formants to fall between harmonics. In such a case, the acoustics of the vocal tract go against the needs for glottal closure. An inappropriate acoustic adjustment interferes with efficient glottal oscillation just as appropriate acoustic adjustments encourage efficiency.
4) Loose phonation: There are many singers who produce a slightly breathy tone at the acoustic passaggi, thinking that they are producing a covered tone. When the tone becomes slightly breathy, it takes on a mellow quality that sounds somewhat like a covered tone. The difference is that in a properly covered tone, the glottal efficiency is maintained, while in loose phonation the glottal efficiency is compromised in order to produce a rounder tone. This glotta adjustment is heard frequently in the top of the male voice and in the middle of the female voice. This inefficient sound has become idiosyncratic among singers today, to the point of being confused for the proper covered tone. This sound does not work well with an orchestra.
I will post example videos and acoustic analysis in the next few days.